1. Field of the Invention
The present invention relates to a thermoplastic resin composition and a production process thereof, and more specifically, to a thermoplastic resin composition comprising a methacrylic resin having a ring structure in the main chain thereof and a glass transition temperature of 110° C. or higher, and a production process thereof.
2. Description of the Related Art
Conventionally, as a resin having transparency, there have been known methacrylic resins. Because methacrylic resins are excellent both in transparency and in surface gloss and weather resistance and have a good balance of mechanical strength, forming processability, and surface hardness, they have widely been used in applications relevant to optics in cars, home electric appliances, and the like. However, the glass transition temperatures of methacrylic resins are about 100° C., and therefore, it has been difficult to use methacrylic resins in the fields requiring heat resistance.
Recently, as a transparent and heat resistant resin having transparency and heat resistance and further having various characteristics such as mechanical strength and forming processability, there have been proposed some lactone ring-containing polymers obtained by subjecting a polymer having hydroxyl groups and ester groups in the molecular chain thereof to lactone cyclization condensation reaction. An example thereof is a polymer in which a copolymer of 2-(hydroxymethyl)acrylic acid alkyl ester and methyl methacrylate or a copolymer of α-hydroxymethyl styrene and methyl methacrylate is subjected to dealcoholization reaction, one kind of transesterification, to give lactone rings by condensation of hydroxyl groups and ester groups present in the same molecule. However, in the conventional methods, an esterification catalyst or a transesterification catalyst such as sulfuric acid or p-toluenesulfonic acid is used in the dealcoholization reaction, and therefore, there has been a problem of coloring of the obtained polymer when the amount of the catalyst is increased in order to raise the dealcoholization reaction rate, and in contrast, if the dealcoholization rate is low, there has been such a problem that the dealcoholization reaction may progress when the obtained polymer is thermally processed, and bubbles or silver streaks may enter into molded articles.
Thus, Japanese Unexamined Patent Publication No. 2001-151814 discloses a technique of reducing the coloring, securing the excellent transparency, and preventing the entering of bubbles or silver streaks into molded articles by using an organophosphorus compound as a catalyst at the time of dealcoholization reaction. Moreover, Japanese Unexamined Patent Publication No. 2000-230016 discloses a technique of making it possible that the dealcoholization reaction rate is extremely high and the remaining volatile matters in the polymer obtained is also few, and therefore, the entering of bubbles or silver streaks into the molded articles is prevented by carrying out dealcoholization reaction in the presence of a solvent and using a devolatilization step together at the time of the above dealcoholization reaction. In addition, Japanese Unexamined Patent Publication No. 2002-138106 discloses a technique of preventing the progress of dealcoholization reaction when thermal processing is carried out, and therefore, the entering of bubbles or silver streaks into molded articles is prevented by converting unreacted hydroxyl groups to groups not acting as dealcoholization reaction points at the time of dealcoholization reaction.